Variable optical attenuator

ABSTRACT

A variable optical attenuator ( 10 ) includes a cover ( 2 ), a housing ( 3 ), an optical module ( 4 ), a reciprocating means ( 5 ), a filter ( 6 ) and a fixer ( 7 ). The filter has a varying optical density gradient and is attached to the reciprocating means. The reciprocating means includes a carrier ( 53 ) mounted to a rotatable screw rod ( 55 ) and a stopper mechanism ( 51 ). When the screw rod is rotated, the carrier with the filter mounted on it moves toward one side of the housing or another. The stopper mechanism halts the carrier ifs side ward movement when it abuts one or another of locating slots ( 31, 32 ) of the housing, preventing the filter from moving too far to either side. Optical signals coming from the input optical fiber ( 45 ) pass through a collimator ( 43 ), through the filter, and are reflected by the reflector ( 42 ) to pass again through the filter and collimator for output in the output optical fiber ( 46 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a variable optical attenuatorfor use in optical fiber communication and optical network, andparticularly to a variable optical attenuator with a stopper mechanism.A cross reference is shown in the copending application have the sametitle, the same inventor and the same assignee filed on Aug. 27, 2001with an unknown serial number.

[0003] 2. Description of Related Art

[0004] An optic attenuator is a passive optical component for reducingoptical power propagating in a fiber, and may perform fixed or variableattenuation of optical signal. Optical attenuators are widely used inoptical transmission and optical networks.

[0005] A general variable optical attenuator comprises a filter. Thefilter has an effective filter region located in an optical path betweena collimator and a reflector. The filter has a filter density whichincreases from a low density region to a high density region. An opticalsignal can be attenuated to different extents by transmitting throughdifferent region of the filter.

[0006] For example, U.S. Pat. No. 4,702,549 describes a variable opticalattenuator comprising two optical fibers having ends aligned to eachother and a filter element mounted on a reciprocating means forselectively positioning the filter element between the fiber ends. Thefilter is not perpendicular to the axis of alignment of the fiber ends.The variable attenuator has a manual screw rod to control theattenuation of the transmitted light. A problem with the conventionalattenuator is that no stopper is incorporated in the attenuator.Controlling the angular position of the screw rod while rotating thescrew rod near the highest and lowest attenuation positions isdifficult. The screw rod may be over rotated near the highest and lowestattenuation position. Devices of U.S. Pat. Nos. 4,989,938 and 4,904,044share the same problem.

[0007] U.S. Pat. Nos. 6,144,794 and 6,130,984 each describe a variableoptical attenuator using reciprocating means to adjust the position ofthe filter. Both devices employ an electrical control system. Althoughthe electrical control systems operate with higher precision, their costis high and they greatly increase the size of the devices.

[0008] The present invention provides a variable optical attenuatorcomprising a stopper structure for preventing a reciprocating movementmeans from over movement beyond the highest and lowest attenuationpositions.

BRIEF SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide an improvedvariable optical attenuator having a stopper mechanism for preventingthe filter from moving beyond end-point positions.

[0010] A variable optical attenuator of the present invention comprisesa housing to which a cover is attached for defining an interior spaceforming an inner cavity in a lower portion of the housing. A pair oflocating slots is defined in opposite lateral sides of the inner cavity.An inner sidewall forms a forward boundary of the inner cavity. A sidehole communicates between one of the locating slots and an outside wallof the housing. A fixing groove and a supporting portion are formedadjacent the other locating slot.

[0011] An optical module is accommodated in the interior space andcomprises a frame, a reflector and a collimator. The frame has a groovewith an inner wall, and a through hole communicating with the groove.The reflector is fixed on the inner wall of the frame and is disposedcoaxially with the through hole. The collimator is positioned in thethrough hole and fixes ends of an input optical fiber for carrying thetransmission optical signals to the attenuator and an output opticalfiber for receiving the resulting attenuated transmission opticalsignals from the attenuator.

[0012] The reciprocating means is accommodated in the inner cavity andcomprises a carrier for carrying a filter, a stopper mechanism, astability mechanism, and a screw rod. The stopper mechanism comprisestwo stopper blocks and a stopper body. The stability mechanism has afixing portion for being fixed to the carrier and a mating portion forcontacting the housing. The screw rod has a threaded portion at itsmiddle and a holding portion at each end.

[0013] When assembled, the carrier moves lengthwise along the screw rodwhen the screw rod is rotated. The filter that is fixed to the carriermoves along with the carrier. The stopper mechanism is formed aroundthree sidewalls of the carrier. The stability mechanism is mounted onthe carrier. The fixing portion of the stability mechanism is insertedinto a fixing groove of the carrier. The mating portion of the stabilitymechanism abuts against the inner sidewall and moves along the innersidewall when the carrier is moved.

[0014] By rotating the screw rod first in one direction and then in thereverse direction, the carrier with the filter can be made to move firsttoward one side and then toward another side of the housing. Thedirection of movement of the filter is perpendicular to the path of theinput and output light. The filter has a filter density which variesbetween a low density region and a high density region along a filteraxis. When the carrier arrives at one end of the screw rod, the stopperabuts with surfaces of the corresponding locating slot and the part ofthe filter penetrated by the input and output light will be either thelow density region or the high density region. During rotation of thescrew rod, the stability mechanism prevents the carrier from rotatingwith the screw rod and provides for stable movement of the filter,thereby ensuring precision adjustment of attenuation of optical signals.

[0015] Other objects, advantages and novel features of the inventionwill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings, wherein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a perspective, up-side-down, assembled view of avariable optical attenuator of the present invention;

[0017]FIG. 2 is an exploded view of the variable optical attenuator ofthe prevent invention;

[0018]FIG. 3 is a partially exploded detail of FIG. 2, without anoptical module or a cover;

[0019]FIG. 4 is an assembled view of FIG. 3 in a first position;

[0020]FIG. 5 is an assembled view of FIG. 3 in a second position; and

[0021]FIG. 6 is an assembled view of FIG. 3 in a third position.

DETAILED DESCRIPTION OF THE INVENTION

[0022] As shown in FIGS. 1-3, a variable optical attenuator 10 of thepresent invention comprises a cover 2, a housing 3, an optical module 4,a reciprocating means 5, a filter 6 and a fixer 7. The housing 3 has aninner cavity 37 and a pair of locating slots 31, 32 positioned at eachside of and communicating with the inner cavity 37. An inner sidewall 33defines a front wall of the inner cavity 37. A side hole 34 ispositioned at one side (not labeled) of the inner cavity 37 andcommunicates between the inner cavity 37 and an outer side of thehousing 3. A fixing groove 36 is separated from the inner cavity 37 bytwo halves of a supporting portion 35, which are formed at a second side(not labeled) of the inner cavity 37. The fixing groove 36 communicateswith the inner cavity 37 via a passageway (not labeled) defined betweenthe two halves of the supporting portion 35.

[0023] The optical module 4 comprises a frame 41, a reflector 42 and acollimator 43. The frame 41 has a groove 47 defined through a middlethereof between an upper side (not labeled) and a lower side (notlabeled) of the frame 41. An inner wall 48 defines a rear side (notlabeled) of the groove 47. A through hole 44 is defined from a frontside (not labeled) of the frame 41 to the groove 47. The reflector 42 isfixed to the inner wall 48 of the frame 41 and is disposed coaxiallywith the through hole 44. An input optical fiber 45 and an outputoptical fiber 46 are fixed to the collimator 43, which is fixed in thethrough hole 44.

[0024] The reciprocating means 5 for moving the variable optical filter6 comprises a carrier 53, a stability mechanism 54, a stopper mechanism51, and a screw rod 55. The carrier 53 carries the filter 6 and ismounted on the screw rod 55. The carrier 53 has a lower plate 533 and anupper plate 532 extending rearward. A fixing groove 534 is defined in aforward surface of the carrier 53. Teeth 531 are formed on an uppersurface of the lower plate 533 and a lower surface of the upper plate532. The stopper mechanism 51 comprises a stopper body 515, a firststopper block 511, and a second stopper block 512. Each stopper block511, 512 has a screw hole 513, 514. The stopper mechanism 51 is used toprevent the carrier 53 from moving too far to either side of the screwrod 55. The stability mechanism 54 can be, for instance, a springmember. The stability mechanism 54 has a mating portion 541, a fixingportion 542, and a resilient connecting portion 544 between the matingand fixing portions 541, 542. The fixing portion 542 has a plurality ofteeth 545. The screw rod 55 has a threaded portion 551 formed along amiddle portion thereof and a holding portion 552 at each end thereof.

[0025] The filter 6 has a varying optical density gradient along atleast one of its dimensions. The filter density varies between a lowdensity region and a high density region along a linear filter axisparallel to a movement path of the filter.

[0026] In assembly, the stopper mechanism 51 is positioned around threesides of the carrier 53. The screw rod 55 is threadedly engaged with andextends through the first screw hole 513, between and lower plate 533and the upper plate 532, and through the second screw hole 514. In thiscondition, the threaded portion 551 engages with the teeth 531 of theupper and lower plates 532, 533 of the carrier, and with threads in thescrew holes 513, 514 of the stopper mechanism 51. The filter 6 is fixedonto the carrier 53. The fixing portion 542 of the stability mechanism54 is inserted into the fixing groove 534 so that the teeth 545 have aninterferential fit with the fixing groove 534. One holding portion 552of the screw rod 55 is inserted into the side hole 34 of the housing 3.The other holding portion 552 is disposed in the passageway (notlabeled) between the two halves of the supporting portion 35 and extendsinto the fixing groove 36. The carrier 53 is thereby positioned withinthe inner cavity 37 and the mating portion 541 of the stabilitymechanism 54 resiliently presses against the inner sidewall 33 of thehousing 3. The mating portion 541 moves along the inner sidewall 33 whenthe carrier 53 moves. The fixer 7 is then assembled in the fixing groove36, positioned on the holding portion 552 of the screw rod 55, so thescrew rod 55 is stably fixed. The screw rod 55 is rotatable about alongitudinal axis thereof. The optical module 4 is assembled in thehousing 3 with the filter 6 protruding into the groove 47 in front ofthe reflector 42. The input optical fiber 45 and output optical fiber 46protrude from a front end of the housing 3. The cover 2 is fixed to atop surface of the housing 3.

[0027] Referring to FIGS. 4-6, in use, optical signals are transmittedfrom the input optical fiber 45 through the collimator 43 and throughthe groove 47 to pass through the filter 6. These optical signals arereflected by the reflector 42, and pass again through the filter 6 andthe collimator 43, in a reverse direction, and are transmitted throughthe output optical fiber 46. When the screw rod 55 is rotated in onedirection, the reciprocating means 5 and the filter 6 move toward thelocating slot 32. When the screw rod 55 is rotated in an oppositedirection, the reciprocating means 5 and the filter 6 move toward thelocating slot 31. The direction of movement of the filter 6 isperpendicular to the path of the input and output optical signals. Thefilter 6 has an optical density gradient which varies between a lowerdensity region and a higher density region along a direction parallel tothe direction of movement of the filter. When the carrier 53 moves toeither end of the screw rod 55, a stopper block 511, 512 of the stoppermechanism 51 abuts against the surface of a locating slot 32, 31respectively. When the stopper block 511 abuts an outside surface of thelocating slot 32, or the other stopper block 512 abuts an outsidesurface of the locating slot 31, the filter 6 penetrated by the inputand output optical signals stops its motion.

[0028] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A variable optical attenuator for attenuating optical signals inputfrom an input fiber and output to an output fiber, comprising: ahousing; a variable optical filter having a filter density gradientvarying between a low density region and a high density region along afilter axis, parallel to a movement path of the filter, the movementpath of the filter being perpendicular to the axis of the input fiberand the output fiber; and a reciprocating means defining a carrier towhich the variable optical filter is mounted, the reciprocating meansproviding a movement of the variable optical filter along the movementpath of the filter, the reciprocating means having a stopper mechanism,being not integrally formed with said carrier, to prevent thereciprocating means from moving the filter beyond a predeterminedextreme point; wherein when the variable optical filter is actuated tomove along the movement path of the filter, an intersection point of theoptical signal with the variable optical filter moves between the lowdensity region and the high density region along the filter axis.
 2. Thevariable optical attenuator as claimed in claim 1 further comprising anoptical module, the optical module comprising a frame.
 3. The variableoptical attenuator as claimed in claim 2, wherein the frame has a groovedefined through at least one side of the frame and a through holedefined through another side of the frame and in communication with thegroove.
 4. The variable optical attenuator as claimed in claim 3 furthercomprising a collimator, the collimator fixing ends of the input fiberand the output fiber and being positioned in the through hole.
 5. Thevariable optical attenuator as claimed in claim 4 further comprising areflector fixed to an inner wall of the groove opposite to andsubstantially normal to an axis of the collimator.
 6. The variableoptical attenuator as claimed in claim 5, wherein the filter ispositioned between the reflector and the collimator.
 7. The variableoptical attenuator as claimed in claim 1, wherein the carrierthreadingly engages a screw rod for being driven along the movementpath, a stability mechanism being attached to the carrier for preventingrotation of the carrier. 8.The variable optical attenuator as claimed inclaim 7 further comprising a fixer for fixing the screw rod in placewithin the housing.
 9. The variable optical attenuator as claimed inclaim 1, wherein the stopper has a stopper body and two stopper blocks.10. The variable optical attenuator as claimed in claim 7, wherein thestopper mechanism is formed around three sidewall of the carrier.
 11. Avariable optical attenuator for attenuating optical signals input froman input fiber and output to an output fiber, comprising: a housing; avariable optical filter having a filter density gradient varying betweena low density region and a high density region along a filter axis,parallel to a movement path of the filter, the movement path of thefilter being perpendicular to the axis of the input fiber and the outputfiber; and a reciprocating means defining a carrier to which thevariable optical filter is mounted, the reciprocating means providing amovement of the variable optical filter along the movement path of thefilter; and a stopper mechanism, being not integrally formed with thecarrier, preventing the reciprocating means from moving the filterbeyond a predetermined extreme point; wherein when the variable opticalfilter is actuated to move along the movement path of the filter, anintersection point of the optical signal with the variable opticalfilter moves between the low density region and the high density regionalong the filter axis.
 12. A variable optical attenuator for attenuatingoptical signals input from an input fiber and output to an output fiber,comprising: a housing; a variable optical filter having a filter densitygradient varying between a low density region and a high density regionalong a filter axis, parallel to a movement path of the filter, thevariable optical filter being moveably positioned in the path definedbetween the input fiber and the output fiber; and a reciprocating meansdefining a carrier to which the variable optical filter is mounted, thereciprocating means providing a movement of the variable optical filteralong the movement path of the filter, the reciprocating means having astopper mechanism, being not integrally formed with the carrier but withportions located at two opposite ends of said carrier along a directionof the movement path of the filter, to prevent the reciprocating meansfrom moving the filter beyond a predetermined extreme point; whereinwhen the reciprocating means actuates the variable optical filter tomove along the movement path of the filter, an intersection point of theoptical signal with the variable optical filter moves between the lowdensity region and the high density region along the filter axis.